The following U.S. patents and patent applications are hereby incorporated herein by reference.
U.S. Pat. No. 6,821,168 discloses an outboard motor provided with an internally contained cylinder and moveable piston. The piston is caused to move by changes in differential pressure between first and second cavities within the cylinder. By adding a hydraulic pump and a steering valve, the hydraulic steering system described in U.S. Pat. No. 6,402,577 is converted to a power hydraulic steering system by adding a hydraulic pump and a steering valve to a manual hydraulic steering system.
U.S. Pat. No. 7,150,664 discloses a steering actuator system for an outboard motor that connects an actuator member to guide rails, which are, in turn, attached to a motive member such as a hydraulic cylinder. The hydraulic cylinder moves along a first axis with the guide rail extending in a direction perpendicular to the first axis. An actuator member is movable along the guide rail in a direction parallel to a second axis and perpendicular to the first axis. The actuator member is attached to a steering arm of the outboard motor.
U.S. Pat. No. 7,255,616 discloses a steering system for a marine propulsion device that eliminates the need for two support pins and provides a hydraulic cylinder with a protuberance and an opening which cooperate with each other to allow a hydraulic cylinder's system to be supported by a single pin for rotation about a pivot axis. The single pin allows the hydraulic cylinder to be supported by an inner transom plate in a manner that it allows it to rotate in conformance with movement of a steering arm of a marine propulsion device.
U.S. Pat. No. 7,467,595 discloses a method for controlling the movement of a marine vessel including rotating one of a pair of marine propulsion devices and controlling the thrust magnitudes of two marine propulsion devices. A joystick is provided to allow the operator of the marine vessel to select port-starboard, forward-reverse, and rotational direction commands that are interpreted by a controller which then changes the angular position of at least one of a pair of marine propulsion devices relative to its steering axis.
U.S. Pat. No. 8,046,122 discloses a control system for a hydraulic steering cylinder utilizing a supply valve and a drain valve. The supply valve is configured to supply pressurized hydraulic fluid from a pump to either of two cavities defined by the position of a piston within the hydraulic cylinder. A drain valve is configured to control the flow of hydraulic fluid away from the cavities within the hydraulic cylinder. The supply valve and the drain valve are both proportional valves in a preferred embodiment of the disclosed invention in order to allow accurate and controlled movement of a steering device in response to movement of a steering wheel of a marine vessel.
U.S. Pat. No. 8,512,085 discloses a tie bar apparatus for a marine vessel having at least first and second marine drives. The tie bar apparatus comprises a linkage that is geometrically configured to connect the first and second marine drives together so that during turning movements of the marine vessel, the first and second marine drives steer about respective first and second vertical steering axes at different angles, respectively.
Unpublished U.S. patent application Ser. No. 14/177,762, filed Feb. 11, 2014, discloses a system for controlling movement of a plurality of drive units on a marine vessel having a control circuit communicatively connected to each drive unit. When the marine vessel is turning, the control circuit defines one of the drive units as an inner drive unit and another of the drive units as an outer drive unit. The control circuit calculates an inner drive unit steering angle and an outer drive unit steering angle and sends control signals to actuate the inner and outer drive units to the inner and outer drive unit steering angles, respectively, so as to cause each of the inner and outer drive units to incur substantially the same hydrodynamic load while the marine vessel is turning. An absolute value of the outer drive unit steering angle is less than an absolute value of the inner drive unit steering angle.